We propose to investigate the importance of mitochondrial biogenesis in the evolution of organ dysfunction in sepsis. Multiple organ dysfunction syndrome (MODS) is a frequent complication of sepsis, and although sepsis mortality increases almost linearly with the number of organs involved, the underlying pathogenesis of organ failure and how it resolves are not understood. We have shown in animals with sepsis that damage to mitochondria in tissues contributes to abnormalities in cellular energy production and, when repair mechanisms fail, to cell death and organ dysfunction (6-12). This is balanced by mitochondrial biogenesis, the adaptive program that maintains the capacity for mitochondrial energy production through maintenance and repair of mitochondrial components and through synthesis of new organelles. We hypothesize that mitochondrial damage is an early finding in patients with severe sepsis and that the extent of mitochondrial injury predicts the severity of sepsis-induced MODS. We propose that the resolution of MODS in sepsis depends on the initiation of mitochondrial biogenesis. The mitochondrial genome is a particularly sensitive target for oxidative injury in sepsis because it is located close to the site of oxidative phosphorylation and is relatively unprotected by anti-oxidant defenses (13-15). Our preliminary data show that mitochondrial DNA (mtDNA) injury and biogenesis are an intrinsic part of the host response to severe infection. To determine how these relate to the development and resolution of MODS in patients, we propose the following Specific Aims: Specific Aim 1. Determine if mitochondrial DNA damage in peripheral blood mononuclear cells (PBMC) predicts organ dysfunction in non-diabetic and diabetic septic patients, especially critical care myopathy. Specific Aim 2. Determine if activation of the molecular mechanisms of mitochondrial DNA replication and biogenesis in PBMC predicts recovery from sepsis-induced organ dysfunction. Specific Aim 3. Determine whether specific molecular pathways are critical to resolution of sepsis- induced organ injury in wild type and diabetic mice. We will characterize mitochondria in PBMC from septic patients to determine the relationship between mtDNA damage and biogenesis to disease severity and outcome. Using a clinically relevant animal model of sepsis, we will investigate pathways important for mitochondrial biogenesis and recovery of organ function and determine whether these are feasible targets for effecting recovery of MODS in septic patients. The results will provide a new approach to the clinical assessment of energy failure during sepsis, stratify patient risk for sepsis complications and use the results to enhance existing animal models, and identify patients who might benefit from therapeutic interventions that promote mitochondrial biogenesis. PUBLIC HEALTH RELEVANCE: The multiple organ dysfunction syndrome (MODS) is a frequent complication of sepsis from severe infections, with ~750,000 reported cases per year and an overall mortality rate of about 30%. Mortality is directly related to severity of organ failure, but the underlying causes and what determines resolution are not understood. These studies will investigate the role of mitochondrial injury and biogenesis in the pathogenesis of organ dysfunction in sepsis, and should lead to new therapies to enhance recovery from organ failures in sepsis.